1. Field of the Invention
The present invention relates to an optical conversion member (also referred to as a wavelength conversion member), and specifically, relates to an optical conversion member which contains a quantum dot and has a high light extraction efficiency.
Further, the present invention also relates to a method for manufacturing the optical conversion member, a backlight unit including the optical conversion member, and a liquid crystal display device including the backlight unit.
2. Description of the Related Art
A flat panel display such as a liquid crystal display device (hereinafter, also referred to as LCD) has been widely used annually as a space saving image display device having low power consumption. The liquid crystal display device is configured of at least a backlight and a liquid crystal cell, and typically, includes members such as a backlight side polarizing plate and a visible side polarizing plate.
In the flat panel display market, improvements in color reproducibility have progressed as LCD performance has improved. From this viewpoint, recently, a quantum dot (also referred to as QD) has attracted attention as a light emission material (refer to US2012/0113672A1). For example, in a case where excitation light is incident on an optical conversion member containing a quantum dot from a backlight, the quantum dot is excited and emits fluorescent light. Here, by using quantum dots having different light emission properties, white light is able to be embodied by emitting each bright line light of red light, green light, and blue light (in a case where a red color is R, a green color is G, and a blue color is B, RGB). In particular, recently, many technologies have been proposed in which a blue light emitting diode is used as a light source, and quantum dots emitting red light and green light are used as fluorescent light, and thus, white light is obtained. The fluorescent light due to the quantum dot has a small half-width of a light emission profile, and thus, white light to be obtained has a high brightness and an excellent color reproducibility. According to the progress of three-wavelength light source technology using such a quantum dot, a color reproduction range has widened to 100% from 72% of the current TV standard (Full High Definition (FHD), National Television System Committee (NTSC)) ratio.
As described above, the quantum dot is a useful material which is able to enhance the performance of LCD by improving color reproducibility. However, currently, the quantum dot is not a material which is available at a low price, and thus, a liquid crystal display device using the quantum dot tends to be expensive. For this reason, in order to reduce the costs of the liquid crystal display device, it is desirable that a light emission efficiency increases such that the use amount of the quantum dot is able to be reduced.
Here, a plurality of configurations such as a sheet type optical conversion member and a bar type optical conversion member have been known as an optical conversion member using a quantum dot, and the sheet type optical conversion member is preferably used from the viewpoint of stability of the quantum dot (refer to US2012/0113672A1). In the sheet type optical conversion member, the quantum dot in a matrix emits light and allows total reflection to occur on the interface with the air, and thus, a part of light (a waveguide mode repeating total reflection) is not able to be extracted to the outside. For this reason, in a case of increasing a light emission efficiency of the sheet type optical conversion member, it is necessary to increase not only a light emission intensity of a light emission body, but also a light extraction efficiency by avoiding the waveguide mode repeating the total reflection.
Various methods such as method of performing isotropic light scattering by dispersing spherical particles in an optical conversion layer, a method of performing isotropic light scattering by applying an isotropic light scattering layer in which spherical particles are dispersed onto an optical conversion layer (refer to FIG. 2), and a method of providing a surface structure in which light scattering is able to be performed are disclosed in US2012/0113672A1 as a method of increasing the light extraction efficiency of the sheet-like optical conversion member using the quantum dot.